1. Field of the Invention
The invention relates to silicone resin compositions and use of these for the production of optical semiconductor elements.
2. Description of the Related Art
The requirements placed upon potting compositions for the production of electrical and electronic components, in particular for the production of optical semiconductor elements such as high-power LEDs (light emitting devices) are very extensive and to some extent contradictory, the aim being to ensure high light yield and lifetime from the LED. Examples of desired properties are:                good surface hardness and shaping properties;        together with flexibility;        good lightfastness and good thermal stability;        good weathering resistance;        low gas transmission and thus avoidance of corrosion;        high transparency;        high refractive index;        no yellowing (discoloration due to heat);        good processing properties;        easy and therefore cost-efficient compositions and, resulting therefrom, greater cost-efficiency in LED production methods.        
The prior art hitherto has already disclosed many proposed solutions, but none of these has ever been capable of satisfying every detail of these requirements.
Many documents disclose the use of addition-crosslinking silicone compositions for the production of LEDs. They are composed of at least one organopolysiloxane having at least two aliphatically unsaturated groups in the molecule, and also of at least one organohydropolysiloxane having two or more Si—H groups in the molecule, and of at least one hydrosilylation catalyst, and frequently of other additives.
The following documents cited by way of example are concerned with proposed solutions for reducing gas transmission. EP2399961B1, for example, discloses addition-crosslinking silicone resin compositions of this type for LED production where at least one antioxidant has to be present as a further additive. US20120256325A1 discloses silicone resin compositions comprising an aryl silicone resin having at least 2 vinyl groups, an addition catalyst, and also an organohydropolysiloxane mixture composed of two different organohydropolysiloxanes having Si-aryl units within the chain, the first being an organohydropolysiloxane oil having alpha-omega terminal Si—H groups, and the second being a monofunctional organopolyhydrosiloxane oil having only one terminal Si—H group. Disadvantages of both solutions are their relatively complex composition, preparative accessibility that is sometimes problematic, and associated therewith, reduced cost-effectiveness.
WO2004/107458A2 discloses addition-crosslinking organopolysiloxane preparations which can optionally be self-crosslinking, either comprising self-crosslinking organopolysiloxanes which require resin units which comprise, per molecule, not only aliphatically unsaturated groups but also Si—H groups, or comprising an addition-crosslinkable preparation made of organopolysiloxanes which also comprise resin units, and also comprising a hydrosilylation catalyst. DE10359705A1 also discloses addition-crosslinking silicone preparations which also contain a self-crosslinking silicone resin. The disadvantage of the preparations described in these documents is that they are composed exclusively of oligomeric or polymeric polyorganosiloxanes, which makes it much more difficult to establish particular processing properties, especially viscosity, which can vary widely, depending on the desired processing method. The resultant disadvantageous effect is that preparations of this type have to be optimized specifically in each case for a particular processing method, and therefore when new organopolysiloxanes are used for a specific purpose these always require appropriate changes to the processing methods, or vice versa.
There is therefore a need for silicone compositions which can easily be varied, and at the same time comply with the requirements indicated above.